In 1977, the American Society of Civil Engineers designated the Mullan Road a National Historic Civil Engineering Landmark, recognizing it as the first major engineered highway in the Pacific Northwest. The ASCE’s official overview describes the road’s construction, original military purpose, importance during the Idaho and Montana gold rushes, and the surveying and engineering methods used to carry the route across the Rocky Mountains. To view the American Society of Civil Engineers documents that designate the Mullan Road as a National Historic Civil Engineering Landmark: